Trematodes (flukes) US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Trematodes (flukes). These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Trematodes (flukes) US Medical PG Question 1: A 19-year-old woman presents to the emergency department with chronic diarrhea, fatigue, and weakness. She also had mild lower extremity edema. On examination, she was noted to be pale. Blood testing revealed peripheral eosinophilia (60%) and a Hb concentration of 8 g/dL. The stool examination revealed Fasciolopsis buski eggs. Which of the following drugs would most likely be effective?
- A. Albendazole
- B. Oxamniquine
- C. Niclosamide
- D. Praziquantel (Correct Answer)
- E. Bithionol
Trematodes (flukes) Explanation: ***Praziquantel***
- **Praziquantel** is the **drug of choice** for treating trematode infections, including those caused by **Fasciolopsis buski**.
- Its mechanism of action involves increasing the permeability of the parasite's cell membrane to calcium, leading to paralysis and death of the fluke.
- It is highly effective, well-tolerated, and the standard first-line treatment.
*Albendazole*
- **Albendazole** is primarily used for various **nematode (roundworm)** infections, such as ascariasis, hookworm, and trichuriasis.
- While it has some activity against certain cestodes, it is not the first-line treatment for **Fasciolopsis buski**, a **trematode (fluke)**.
*Oxamniquine*
- **Oxamniquine** is an anthelmintic specifically used for the treatment of **schistosomiasis**, particularly against *Schistosoma mansoni*.
- It works by damaging the adult worms' teguments, but it is not effective against **Fasciolopsis buski**.
*Niclosamide*
- **Niclosamide** is an effective treatment for **cestode (tapeworm)** infections, such as *Taenia saginata* and *Hymenolepis nana*.
- Its mechanism involves inhibiting parasitic mitochondrial oxidative phosphorylation, but it is not active against **fluke** infections like **Fasciolopsis buski**.
*Bithionol*
- **Bithionol** is used primarily for treating **Fasciola hepatica** (the common liver fluke) and **Paragonimus westermani** (lung fluke) infections.
- While it has trematocidal activity, it is **not the drug of choice** for **Fasciolopsis buski**—**praziquantel** is preferred due to its superior efficacy, broader spectrum against intestinal flukes, better safety profile, and widespread availability.
Trematodes (flukes) US Medical PG Question 2: A 67-year-old male presents to his primary care physician for evaluation of fever and an unintended weight loss of 25 pounds over the last 4 months. He also has decreased appetite and complains of abdominal pain located in the right upper quadrant. The patient has not noticed any changes in stool or urine. He emigrated from Malaysia to the United States one year prior. Social history reveals that he smokes half a pack per day and has 5-7 drinks of alcohol per day. The patient is up to date on all of his vaccinations. Physical exam findings include mild jaundice as well as an enlarged liver edge that is tender to palpation. Based on clinical suspicion, biomarker labs are sent and show polycythemia and an elevated alpha fetoprotein level but a normal CA 19-9 level. Surface antigen for hepatitis B is negative. Ultrasound reveals a normal sized gallbladder. Given this presentation, which of the following organisms was most likely associated with the development of disease in this patient?
- A. Naked DNA virus
- B. Enveloped DNA virus
- C. Curved gram-negative bacteria
- D. Acute angle branching fungus
- E. Trematode from undercooked fish (Correct Answer)
Trematodes (flukes) Explanation: ***Trematode from undercooked fish***
- The patient's symptoms (fever, RUQ pain, weight loss, jaundice, hepatomegaly, elevated **AFP**, and normal CA 19-9) point strongly towards **hepatocellular carcinoma (HCC)**.
- The history of emigration from Malaysia and the elevated **alpha-fetoprotein (AFP)** despite negative hepatitis B antigen, suggest a parasitic infection, specifically a liver fluke (trematode), as a risk factor for HCC. **Clonorchis sinensis** and **Opisthorchis viverrini** are trematodes acquired from undercooked freshwater fish, endemic to Southeast Asia, and are known to cause cholangiocarcinoma and, less commonly, HCC.
*Naked DNA virus*
- This typically refers to viruses like **human papillomavirus (HPV)** or **adenovirus**, which are not primary causes of the described liver pathology or HCC with this specific presentation.
- While some naked DNA viruses can cause human disease, they are not typically linked to the patient's specific symptoms and lab findings (elevated AFP) in the context of liver cancer from a Southeast Asian background.
*Enveloped DNA virus*
- This category includes viruses like **Herpesviruses** and **Hepatitis B virus (HBV)**. While HBV is a major cause of HCC, the patient's hepatitis B surface antigen is negative, ruling out active or chronic HBV infection as the direct cause in this case.
- Other enveloped DNA viruses do not commonly cause this specific cluster of symptoms and risk factors for HCC.
*Curved gram-negative bacteria*
- This description often refers to bacteria like **Campylobacter** or **Helicobacter pylori**. These can cause gastrointestinal issues but are not typically associated with liver masses, jaundice, and elevated AFP in the context of HCC.
- They do not explain the patient's risk factors or presentation that strongly suggests chronic liver inflammation leading to cancer.
*Acute angle branching fungus*
- This refers to fungi like **Aspergillus**, which can cause invasive infections, particularly in immunocompromised individuals.
- While Aspergillus can cause pulmonary infections and, less commonly, disseminate to other organs including the liver, it does not typically present with the described risk factors (Southeast Asian origin, undercooked fish consumption) or lab findings (elevated AFP) for HCC, nor does it fit the general clinical picture.
Trematodes (flukes) US Medical PG Question 3: A 30-year-old man presents to the physician after he discovered a raised, red, string-shaped lesion beneath the skin on his right foot. The lesion seems to move from one location to another over the dorsum of his foot from day to day. He says that the lesion is extremely itchy and has not responded to over the counter topical treatment. He and his wife recently returned from a honeymoon in southern Thailand, where they frequented the tropical beaches. The physician diagnoses him with a parasitic infection and prescribes albendazole for the patient. With which of the following organisms is the patient most likely infected?
- A. Ancylostoma braziliense (Correct Answer)
- B. Dracunculus medinensis
- C. Necator americanus
- D. Strongyloides stercoralis
- E. Wuchereria bancrofti
Trematodes (flukes) Explanation: ***Ancylostoma braziliense***
- This clinical presentation of a **pruritic, migratory, serpiginous rash** on the foot after exposure to contaminated sand (tropical beach in Thailand) is classic for **cutaneous larva migrans**, caused by hookworm larvae, predominantly *Ancylostoma braziliense*.
- The larvae penetrate the skin but cannot complete their life cycle in humans, instead migrating subcutaneously, causing the characteristic **"creeping eruption"**.
*Dracunculus medinensis*
- This parasite causes **dracunculiasis**, where the adult female worm migrates to the skin, creating a painful blister, often on the lower limbs, from which it emerges.
- It is acquired by ingesting **copepods** (water fleas) containing larvae, not by direct contact with contaminated sand, and the lesion typically ulcerates rather than migrating repeatedly.
*Necator americanus*
- This is a human hookworm that causes **iron deficiency anemia** and can lead to **cutaneous larva currens** from larval penetration, which is a rapidly advancing linear lesion, but it typically progresses to systemic infection where the worms reside in the small intestine.
- While it can cause an itchy rash at the site of penetration (ground itch), it does not cause the **chronic, migratory, serpiginous eruption** characteristic of cutaneous larva migrans.
*Strongyloides stercoralis*
- This parasite can cause **larva currens** (a rapidly moving linear skin eruption) and systemic complications, particularly in immunocompromised individuals.
- While it can cause skin lesions, the typical description is of a much faster-moving lesion that usually spreads from the anus and is less serpiginous and persistent in one area compared to the classic presentation of cutaneous larva migrans.
*Wuchereria bancrofti*
- This nematode causes **lymphatic filariasis** (elephantiasis), characterized by lymphedema, hydrocele, and chyluria, and is transmitted by **mosquito bites**.
- It does not cause cutaneous migratory lesions on the foot; its pathology relates to chronic lymphatic obstruction by adult worms.
Trematodes (flukes) US Medical PG Question 4: A 68-year-old man presents to his physician for symptoms of chronic weight loss, abdominal bloating, and loose stools. He notes that he has also been bothered by a chronic cough. The patient’s laboratory work-up includes a WBC differential, which is remarkable for an eosinophil count of 9%. Stool samples are obtained, with ova and parasite examination revealing roundworm larvae in the stool and no eggs. Which of the following parasitic worms is the cause of this patient’s condition?
- A. Taenia saginata
- B. Taenia solium
- C. Strongyloides stercoralis (Correct Answer)
- D. Necator americanus
- E. Ascaris lumbricoides
Trematodes (flukes) Explanation: ***Strongyloides stercoralis***
- The presence of **larvae (rhabditiform)** in the stool, **pulmonary symptoms** (chronic cough), **gastrointestinal symptoms** (weight loss, bloating, loose stools), and **eosinophilia** are classic findings for *Strongyloides stercoralis* infection.
- Unlike most other intestinal nematodes, *Strongyloides* can establish an **autoinfection cycle**, meaning larvae can reinfect the host, leading to persistent and potentially severe infections even in immunocompetent individuals, without the need for external re-exposure or eggs in stool.
*Taenia saginata*
- This is a **tapeworm (cestode)** that causes taeniasis and is acquired by consuming undercooked beef.
- Diagnosis is typically made by finding **proglottids** or **eggs** in the stool, not larvae, and pulmonary symptoms are not characteristic.
*Taenia solium*
- This is another **tapeworm (cestode)**, acquired by consuming undercooked pork; it can cause taeniasis (intestinal infection) and cysticercosis (tissue infection).
- Similar to *T. saginata*, diagnosis involves finding **proglottids** or **eggs** in stool for intestinal infection, and it does not typically present with lung involvement or larvae in stool.
*Necator americanus*
- This is a **hookworm** that causes iron-deficiency anemia due to blood loss in the intestines.
- While it can cause some pulmonary symptoms as larvae migrate through the lungs, and gastrointestinal symptoms, the diagnostic hallmark is finding **eggs** in the stool, not larvae.
*Ascaris lumbricoides*
- This is the **giant roundworm**; infections are common and often asymptomatic, but heavy worm burdens can cause intestinal obstruction or malnutrition.
- While **pulmonary symptoms (Loeffler's syndrome)** can occur during larval migration, and eosinophilia is present, the diagnosis is confirmed by finding characteristic **mammillated eggs** in the stool, not larvae.
Trematodes (flukes) US Medical PG Question 5: A 32-year-old woman presents to your office with abdominal pain and bloating over the last month. She also complains of intermittent, copious, non-bloody diarrhea over the same time. Last month, she had a cough that has since improved but has not completely resolved. She has no sick contacts and has not left the country recently. She denies any myalgias, itching, or rashes. Physical and laboratory evaluations are unremarkable. Examination of her stool reveals the causative organism. This organism is most likely transmitted to the human host through which of the following routes?
- A. Insect bite
- B. Penetration of skin (Correct Answer)
- C. Sexual contact
- D. Inhalation
- E. Animal bite
Trematodes (flukes) Explanation: ***Penetration of skin***
- The symptoms of **abdominal pain**, **bloating**, **intermittent copious non-bloody diarrhea**, and a recent **cough** are highly suggestive of a **hookworm infection**.
- Hookworm larvae (filariform larvae) primarily penetrate the skin, usually through bare feet, as their mode of entry into the human host.
*Insect bite*
- Although some parasitic infections are transmitted by insect bites (e.g., malaria, Chagas disease), hookworms are not transmitted this way.
- **Insect-borne diseases** typically present with different clinical manifestations or geographical associations.
*Sexual contact*
- **Sexually transmitted infections** involve direct contact of mucous membranes or body fluids during sexual activity.
- Hookworm infection transmission through sexual contact is not a recognized route.
*Inhalation*
- **Inhalation** is a route of transmission for respiratory pathogens (e.g., influenza, tuberculosis) or certain fungal infections, but not for hookworms.
- While hookworm larvae migrate through the lungs, the initial infection pathway is not via inhalation.
*Animal bite*
- **Animal bites** transmit diseases like rabies or certain bacterial infections, but not parasitic hookworms.
- Hookworm infection does not result from direct contact with an animal's saliva or puncture wound.
Trematodes (flukes) US Medical PG Question 6: A 45-year-old male presents to the emergency room complaining of severe nausea and vomiting. He returned from a business trip to Nigeria five days ago. Since then, he has developed progressively worsening fevers, headache, nausea, and vomiting. He has lost his appetite and cannot hold down food or water. He did not receive any vaccinations before traveling. His medical history is notable for alcohol abuse and peptic ulcer disease for which he takes omeprazole regularly. His temperature is 103.0°F (39.4°C), blood pressure is 100/70 mmHg, pulse is 128/min, and respirations are 22/min. Physical examination reveals scleral icterus, hepatomegaly, and tenderness to palpation in the right and left upper quadrants. While in the examination room, he vomits up dark vomitus. The patient is admitted and started on multiple anti-protozoal and anti-bacterial medications. Serology studies are pending; however, the patient dies soon after admission. The virus that likely gave rise to this patient’s condition is part of which of the following families?
- A. Togavirus
- B. Flavivirus (Correct Answer)
- C. Calicivirus
- D. Hepevirus
- E. Bunyavirus
Trematodes (flukes) Explanation: ***Flavivirus***
- The clinical presentation, including acute onset of **high fever**, headache, nausea, vomiting (**dark vomitus**), **scleral icterus**, and **hepatomegaly** following travel to Nigeria, is highly suggestive of **yellow fever**.
- Yellow fever is caused by the **yellow fever virus**, which is a **flavivirus** transmitted by mosquitoes, primarily *Aedes aegypti*.
*Togavirus*
- The Togavirus family includes viruses like **rubella virus** and **alphaviruses** (e.g., Eastern equine encephalitis virus).
- While some alphaviruses can cause fever and encephalitis, they typically do not present with the characteristic **hemorrhagic fever** and severe liver involvement seen in this case.
*Calicivirus*
- The Calicivirus family includes **Norovirus**, which is a common cause of **gastroenteritis** with vomiting and diarrhea.
- Norovirus infections are typically self-limiting and do not usually lead to the severe systemic symptoms, **jaundice**, or fatal outcome described here.
*Hepevirus*
- The Hepevirus family includes the **hepatitis E virus (HEV)**.
- HEV causes **acute viral hepatitis**, characterized by jaundice, nausea, and vomiting, but it rarely progresses to the rapid, severe, and fatal hemorrhagic form seen in this patient.
*Bunyavirus*
- The Bunyavirus family (now split into several families) includes viruses like Hantavirus and Rift Valley fever virus, which can cause **hemorrhagic fevers**.
- While some bunyaviruses are found in Africa, the specific constellation of symptoms, particularly the prominent **scleral icterus** and rapid progression to severe liver failure and death, is most consistent with **yellow fever**, a flavivirus.
Trematodes (flukes) US Medical PG Question 7: A 45-year-old man with a history of poorly controlled human immunodeficiency virus (HIV) infection presents to the emergency room complaining of clumsiness and weakness. He reports a 3-month history of worsening balance, asymmetric muscle weakness, and speech difficulties. He recently returned from a trip to Guatemala to visit his family. He has been poorly compliant with his anti-retroviral therapy and his most recent CD4 count was 195. His history is also notable for rheumatoid arthritis and hepatitis C. His temperature is 99°F (37.2°C), blood pressure is 140/90 mmHg, pulse is 95/min, and respirations are 18/min. On exam, he has 4/5 strength in his right upper extremity, 5/5 strength in his left upper extremity, 5/5 strength in his right lower extremity, and 3/5 strength in his left lower extremity. His speech is disjointed with intermittent long pauses between words. Vision is 20/100 in the left eye and 20/40 in his right eye; previously, his eyesight was 20/30 bilaterally. This patient most likely has a condition caused by which of the following types of pathogens?
- A. Arenavirus
- B. Bunyavirus
- C. Herpesvirus
- D. Polyomavirus (Correct Answer)
- E. Picornavirus
Trematodes (flukes) Explanation: ***Polyomavirus***
- The patient's **poorly controlled HIV**, **low CD4 count (195)**, and progressive neurological symptoms (clumsiness, weakness, speech difficulties, vision changes) are highly suggestive of **Progressive Multifocal Leukoencephalopathy (PML)**.
- PML is caused by the **JC virus**, which is a type of **polyomavirus**, typically reactivating in immunocompromised individuals.
*Arenavirus*
- Arenaviruses (e.g., Lassa fever virus) are known to cause **hemorrhagic fevers** and can lead to neurological complications, but the clinical presentation described (progressive focal neurological deficits in an HIV patient) is not typical for an arenavirus infection.
- While some arenaviruses cause **meningoencephalitis**, the progressive, demyelinating-like course seen in this patient points away from arenavirus.
*Bunyavirus*
- Bunyaviruses (e.g., Hantavirus, La Crosse encephalitis virus) can cause **encephalitis**, fever, and myalgia, but they don't typically present with the specific constellation of **progressive white matter lesions** and focal neurological signs characteristic of PML in an HIV patient.
- Hantaviruses are more associated with **hemorrhagic fever with renal syndrome** or **hantavirus cardiopulmonary syndrome**.
*Herpesvirus*
- While herpesviruses (e.g., HSV, CMV, VZV) can cause severe neurological disease in HIV patients (e.g., **CMV encephalitis**, **HSV encephalitis**, **VZV vasculopathy**), the described progressive multifocal deficits, especially with rapid worsening, in an HIV patient with a low CD4 count strongly favor PML.
- Herpesviral encephalitides often present with more acute onset, fever, and seizures, or specific radiographic patterns not directly matching PML.
*Picornavirus*
- Picornaviruses, such as enteroviruses, can cause **aseptic meningitis** or **encephalitis**, particularly in immunocompromised individuals.
- However, the progressive, multifocal neurological deficits, particularly affecting **white matter**, are not characteristic of picornavirus infections, which tend to cause more diffuse or acute inflammatory processes.
Trematodes (flukes) US Medical PG Question 8: A 27-year-old woman comes to the physician for a 1-week-history of painful urination and urinary frequency. She has no history of serious illness and takes no medications. She is sexually active with her boyfriend. Her temperature is 36.7°C (98.1°F). There is no costovertebral angle tenderness. Urine dipstick shows leukocyte esterase. A Gram stain does not show any organisms. Which of the following is the most likely causal pathogen?
- A. Escherichia coli
- B. Chlamydia trachomatis (Correct Answer)
- C. Gardnerella vaginalis
- D. Neisseria gonorrhoeae
- E. Trichomonas vaginalis
Trematodes (flukes) Explanation: ***Chlamydia trachomatis***
- This patient presents with symptoms of **dysuria** and **urinary frequency**, consistent with a **urethritis**. The absence of bacteria on Gram stain points towards an **atypical pathogen**.
- **Chlamydia trachomatis** is a common cause of **non-gonococcal urethritis** and is a sexually transmitted infection, which fits with the sexually active history.
*Escherichia coli*
- **E. coli** is the most common cause of **bacterial urinary tract infections (UTIs)**, but a Gram stain in this case would typically reveal Gram-negative rods.
- While it causes dysuria and frequency, the **negative Gram stain** makes it less likely than an atypical pathogen.
*Gardnerella vaginalis*
- **Gardnerella vaginalis** is associated with **bacterial vaginosis**, causing a characteristic **fishy odor** and **vaginal discharge**, which are not reported here.
- It does not typically cause urethritis leading to painful urination and urinary frequency.
*Neisseria gonorrhoeae*
- **Neisseria gonorrhoeae** can cause **urethritis** with symptoms similar to those presented, and it is a sexually transmitted infection.
- However, Gram stain would typically show **Gram-negative diplococci** (intracellularly), which were not observed in this case.
*Trichomonas vaginalis*
- **Trichomonas vaginalis** is a **protozoan parasite** causing **trichomoniasis**, which commonly presents with **vaginitis** (frothy, green-yellow discharge, itching) or sometimes urethritis.
- While it is a **sexually transmitted infection**, this organism is not detected by Gram stain (which only stains bacteria); it would require **wet mount microscopy** for visualization. The primary presentation is usually vaginal, and it's less likely to be the sole cause of these urinary symptoms without other signs of vaginitis.
Trematodes (flukes) US Medical PG Question 9: A 4-year-old girl presents with recurrent abdominal pain and a low-grade fever for the past 2 months. The patient’s mother says that she has lost her appetite which has caused some recent weight loss. She adds that the patient frequently plays outdoors with their pet dog. The patient is afebrile and vital signs are within normal limits. On physical examination, conjunctival pallor is present. Abdominal examination reveals a diffusely tender abdomen and significant hepatomegaly. There is also a solid mass palpable in the right upper quadrant measuring about 3 x 4 cm. Laboratory findings are significant for the following:
Hemoglobin (Hb%) 9.9 g/dL
Total count (WBC) 26,300/µL
Differential count
Neutrophils 36%
Lymphocytes 16%
Eosinophils 46%
Platelets 200,000/mm3
Erythrocyte sedimentation rate 56 mm/h
C-reactive protein 2 mg/L
Serum globulins 5 g/dL
Laparoscopic resection of the mass is performed, and a tissue sample is sent for histopathology. Which of the following is the organism most likely responsible for this patient’s condition?
- A. Ancylostoma braziliense
- B. Ascaris lumbricoides
- C. Toxocara canis (Correct Answer)
- D. Trichuris trichiura
- E. Toxocara cati
Trematodes (flukes) Explanation: ***Toxocara canis***
- The child's history of playing outdoors with a pet dog, **eosinophilia**, **hepatomegaly**, abdominal mass, and **elevated globulins** are highly suggestive of **visceral larva migrans (VLM)**, most commonly caused by *Toxocara canis*.
- *Toxocara canis* larvae migrate through human tissues, particularly the liver, causing granuloma formation that can present as palpable masses and systemic symptoms.
*Ancylostoma braziliense*
- This hookworm primarily causes **cutaneous larva migrans**, presenting as an intensely pruritic, serpiginous rash.
- It does not typically cause systemic symptoms like hepatomegaly, abdominal masses, or significant eosinophilia in the way described.
*Ascaris lumbricoides*
- *Ascaris lumbricoides* causes **ascariasis**, primarily manifesting as intestinal symptoms, malnutrition, or pulmonary symptoms during larval migration (Löffler syndrome)
- While it can cause eosinophilia, it rarely presents with solid hepatic masses or the specific constellation of symptoms seen here.
*Trichuris trichiura*
- *Trichuris trichiura* causes **trichuriasis** (whipworm infection), primarily leading to **gastrointestinal symptoms** such as abdominal pain, diarrhea, and rectal prolapse in heavy infections.
- It is not associated with migratory visceral larvae, hepatomegaly, or palpable liver masses.
*Toxocara cati*
- While *Toxocara cati* also causes visceral larva migrans, it is associated with **cats** rather than dogs. The patient's history specifically mentions a pet dog.
- The clinical presentation with hepatomegaly, abdominal mass, and eosinophilia would otherwise be consistent with *Toxocara* infection.
Trematodes (flukes) US Medical PG Question 10: A 35-year-old man from Thailand presents with low-grade fever, chronic cough, and night sweats for 3 months. He describes the cough as productive and producing white sputum that is sometimes streaked with blood. He also says he has lost 10 lb in the last 3 months. Past medical history is unremarkable. The patient denies any smoking history, alcohol, or recreational drug use. The vital signs include blood pressure 115/75 mm Hg, heart rate 120/min, respiratory rate 20/min, and temperature 36.6℃ (97.8℉). On physical examination, the patient is ill-looking and thin with no pallor or jaundice. Cardiopulmonary auscultation reveals some fine crackles in the right upper lobe. A chest radiograph reveals a right upper lobe homogeneous density. Which of the following tests would be most helpful in making a definitive diagnosis of active infection in this patient?
- A. PPD test
- B. Silver stain
- C. Ziehl-Neelsen stain (Correct Answer)
- D. Gram stain
- E. Interferon-gamma assay
Trematodes (flukes) Explanation: ***Ziehl-Neelsen stain***
- The patient's symptoms (low-grade fever, chronic cough with white/bloody sputum, night sweats, weight loss) and chest X-ray findings (right upper lobe homogeneous density) are highly suggestive of **active tuberculosis (TB)**, especially given his origin from Thailand (a country with a high TB burden).
- The **Ziehl-Neelsen stain** (acid-fast stain) directly visualizes **acid-fast bacilli** (AFB) like *Mycobacterium tuberculosis* in sputum, providing a rapid and definitive diagnosis of active infection.
*PPD test*
- A **PPD test** (tuberculin skin test) indicates exposure to *Mycobacterium tuberculosis* but cannot differentiate between **latent TB infection** and **active disease**.
- A positive PPD can occur in individuals previously exposed or vaccinated with BCG, offering no direct evidence of current active infection.
*Silver stain*
- **Silver stain** (e.g., Gomori methenamine silver) is used to identify fungal organisms like *Pneumocystis jirovecii* or certain bacteria, such as *Legionella pneumophila*.
- It is not the primary stain for diagnosing tuberculosis, which requires detection of acid-fast bacilli.
*Gram stain*
- **Gram stain** is used to classify bacteria based on their cell wall properties (Gram-positive or Gram-negative).
- *Mycobacterium tuberculosis* has a unique **mycolic acid-rich cell wall** that makes it resistant to Gram staining and requires acid-fast staining for visualization.
*Interferon-gamma assay*
- An **interferon-gamma release assay (IGRA)**, like the Quantiferon-TB Gold test, detects exposure to *Mycobacterium tuberculosis* and is used to diagnose **latent TB infection**.
- Similar to the PPD test, it cannot distinguish between latent infection and **active disease**, and a positive result requires further investigation for active TB.
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